[Nathan Robinson]

[Rodolfo Martínez]

Well, i´m not a professional fencer too, but i think that the ability of the soldiers have a defining role. You can put a breast plated dopplesoldner with his zweihander against a full armored foot man-at-arms with a longsword/ little shield/dagger, who trained since childhood, but still no one can affirm who would win. A bit of luck and hability is more defining that who have the biggest weapon (You should not laugh in the face of a longsword/ armingsword and shield wielder becouse you have a 6 feet zweihander, he can deliver lighning speed thrusts and blows, and believe me, if he knows what he is doing you should not relly totaly in the lenght of your weapon becouse it your enemy is close to you the sword can betray you). The speed, versatility and grappling habilities of the weapon are very important too. If the swords have XVI century complex hilts they can gain some versatility too.

I think the same goes for two full armored men-at-arms one wielding a longsword and the other the arming sword and shield. The first one should not totaly relly on his sword´s length becouse a professional shield wielder is a very hard opponent as he or she will use the shield not only for defense but for offense too. In the other hand, the longsword knight has more reach and he has a free hand wich he can use as he wants, but again, are luck and ability the principal factors (From my point of view) that determinates the result of our hypothetical duel. But surelly i´m ignoring some points wich a professional fencer would not ignore.
The combat manual Flos Duellatorum shows how a dagger can defeat a longsword, and if i´m not wrong in the Goliath or Gladiatoria there are some techniques with shield too.

I hope i could help you.